SEARCH

SEARCH BY CITATION

Summary

  1. Top of page
  2. Summary
  3. Method
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Using an airway mannequin and artificial lung model, we compared surgical cricothyroidotomy with a 6.0-mm cuffed Portex tracheostomy tube with wire-guided cricothyroidotomy using a 5.0-mm cuffed Melker or 6.0-mm uncuffed Melker tube. The trial was carried out by 27 anaesthetists using a randomised, crossover design. Surgical cricothyroidotomy proved significantly faster (mean (SD) time to first breath 44.3 (12.5) s for Portex surgical, 87.2 (21.6) s for cuffed Melker, 87.8 (19.2) s for uncuffed Melker, p < 0.001). With a standardised ventilator model, the cuffed tubes provided more effective ventilation (mean (SD) tidal volume 446 (41) ml Portex, 436 (52) ml cuffed Melker, 19 (5) ml uncuffed Melker, p < 0.001). Fourteen of the participants preferred the wire-guided system. We conclude that, in this model, a cuffed device is preferable when cricothyroidotomy is needed. In addition, the surgical method is quicker than a wire-guided approach.

In the ‘can’t intubate, can't ventilate' scenario, cricothyroidotomy is recommended if all other methods of ventilation have failed to rapidly restore oxygenation [1]. Several commercial cricothyroidotomy kits are available for use with standard resuscitation apparatus and conventional low-pressure ventilation. Until recently, all used an uncuffed tube. It has been suggested that in ‘can’t intubate, can't ventilate' conditions, upper airway obstruction is usually inspiratory [2, 3], so that an uncuffed airway of 4.0 mm or less provides ineffective positive pressure ventilation because of proximal gas leakage [4], particularly in the poorly compliant lung. To resolve this it has been recommended that expiratory obstruction be created by pinching the mouth and nose or by inserting a mouth-pack. These methods have not been formally assessed. A 6.0-mm wire-guided uncuffed tube provides almost adequate ventilation in the presence of moderate upper airway resistance [4] and restores oxygenation within 2 min in a simulated emergency [5]. Alternatively, a cuffed tube can be inserted by surgical cricothyroidotomy to provide both a secure airway and optimal ventilation. Recently, a cuffed Melker tube has been introduced for small incision, Seldinger wire-guided insertion (Cook, Bloomington, IN) but this device has not been formally assessed. Uncuffed wire guided devices have been compared with surgical cricothyroidotomy, but with conflicting results [6, 7].

We therefore compared surgical cricothyroidotomy with both uncuffed and cuffed Melker Seldinger wire-guided devices in an airway model to understand both the practicalities of insertion and the effectiveness of ventilation, with and without upper airway obstruction.

Method

  1. Top of page
  2. Summary
  3. Method
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

After ethics committee approval, we asked all anaesthetists in the Chester anaesthetics department to volunteer to take part in the study. Twenty-seven agreed to do so. Their grade and previous experience of real and simulated emergency tracheal access was noted and all data were made anonymous.

A VBM Bill 1 airway simulator (VBM Medizintechnik, Gmbh, Sulz, Germany) was connected to an Ohmeda Lung Simulator (Datex Ohmeda, Ltd, Hatfield, Herts., UK) with compliance set to 20 ml.cm−1 H2O, and a Biotek VT Plus Gasflow Analyser (Biotek Instruments Inc., Highland Park, VT) was interposed between them (Fig. 1).

image

Figure 1.  Layout of apparatus.

Download figure to PowerPoint

Each volunteer watched a video clip of both surgical and wire-guided techniques and then live demonstrations of each technique on the model. Surgical cricothyroidotomy was done with a 6.0-mm Portex tracheostomy tube (Smiths Medical Ltd, Hythe, UK) and wire-guided cricothyroidotomy used a 5.0-mm Melker cuffed tube or a 6.0-mm Melker uncuffed device.

The technique of wire-guided cricothyroidotomy was as described in the Melker instructional video [9]. A small vertical skin incision is made over the cricothyroid membrane, followed by needle cricothyroidotomy and aspiration of air. A guidewire is then passed through the needle and the needle removed. A dilator/airway assembly is passed over the guidewire, which is then withdrawn. In the case of the cuffed Melker, the cuff is then inflated.

We taught a technique of conventional surgical cricothyroidotomy [9] modified by using an initial vertical skin incision with a size 20 scalpel to allow accurate palpation of the cricothyroid membrane. A horizontal stab incision is then made through the membrane, which can be slightly extended laterally. The handle of the scalpel is next passed through the incision and rotated 180° in a clockwise and anticlockwise direction. The incision is further dilated with artery forceps if required and the tracheostomy tube firmly pushed through the incision from a lateral direction, rotating through 90° and then advancing caudally. The cuff is then inflated.

The surgical instruments (scalpel, artery forceps, tracheostomy tube and syringe) were placed in a kidney dish and covered with paper. The Melker kits came with a folded paper covering. Timing started when the paper was removed and stopped following first successful ventilation. Timing was carried out using a digital stopwatch measuring to a 1/100th of a second, operated by an observer.

The candidate then attempted surgical cuffed, wire-guided cuffed and wire-guided uncuffed cricothyroidotomy on the model in a random order dictated by the toss of a coin. A new guidewire was used for each wire-guided attempt and an entirely new kit after four insertions. The model larynx was replaced after each surgical attempt. After every airway attempt the artificial skin was moved to ensure there were no visual clues to the location of the cricothyroid membrane for the next attempt.

We noted the candidate's technique preference both before and after the exercise, time to achieve ventilation, number of attempts, complications (e.g. misplacement) and subjective assessment of relative difficulty on a scale of 1 (very easy) to 5 (very difficult). We also noted minute volume, tidal volume and airway pressure with each device using a Penlon Nuffield mechanical ventilator (Penlon Ltd, Abindgon, UK) set to deliver a tidal volume of 500 ml. With the uncuffed tube the same measurements were made in the presence and absence of attempted upper airway obstruction, using mouth and nose occlusion by hand. A self-inflating bag (Laerdal Medical Ltd, Orpington, UK) was also used to assess maximum achievable ventilation, with and without manual obstruction. These measurements were repeated with each candidate.

Ventilation was measured using a Biotek VT Plus gas analyser (Biotek Instruments Inc.) which allowed breath-to-breath measurement of tidal volume, airway pressure and mean minute volume. Following successful ventilation, each candidate delivered 10 breaths while readings stabilised, after which the maximum airway pressure, tidal volume and minute volume were recorded over the next three breaths.

Numerical data were assessed using the Kolmogorov-Smirnov test for normality. Where appropriate, comparison between groups was made using repeated-measures one-way analysis of variance (anova) or paired t-test. Where the data were not normally distributed, Friedman's test for related groups or the Wilcoxon signed-ranks tests were used. Fisher's exact test was used for categorical data.

Results

  1. Top of page
  2. Summary
  3. Method
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Twenty-five of the 27 volunteers had prior training in emergency cricothyroidotomy, mostly on advanced trauma life support (ATLS) courses. Three had experience of actual emergency cricothyroidotomy: one wire-guided and two surgical. Twenty-four had practised on a model, two had practised on cadavers and nine had experience of electively inserting the Mini-Trach (Smiths Medical Ltd, Hythe, UK) or of percutaneous dilational tracheostomy.

The mean (SD) time for insertion of the surgical airway was 44.3 (12.5) s. The surgical airway was inserted significantly more quickly than either of the Melker devices (p < 0.001) (Table 1). The Melker devices were indistinguishable in this respect (p = 0.91).

Table 1.   Insertion times, number of attempts, failures, subjective difficulty and preferences, comparing Melker uncuffed, Melker cuffed and surgical cricothyroidotomy. Difficulty score is (from 1 = very easy to 5 = very difficult). Values are mean (SD) or median [range]. p-values relate to comparisons between all groups except where indicated.
 Melker uncuffedMelker cuffedSurgical 
  • *

    Melker uncuffed vs. Melker cuffed.

Insertion time; s87.8 (19.2)87.2 (21.6)44.3 (12.5)p < 0.001 p = 0.91*
No. of attempts 1 [1–2] 1 [1–2] 1 [1–3]
Failures by grade; n
 Consultant (11) 0 0 0
 Staff Grade (3) 0 0 2
 Registrar (6) 1 1 1
 SHO (7) 0 1 1
 Total (27) 1 2 4 p = 0.25
Difficulty score 3 [1–4] 3 [1–5] 2 [1–4] p = 0.18
Preference; n
 Pre-trial 216 9
 Post-trial 01413

The mean (SD) time for the first Melker insertion (of either variety) was 93.1 (19.2) s and for the 2nd attempt, 81.9 (20.0) s (p = 0.006). The mean difference between the first Melker insertion and the surgical attempt was − 48.8 (17.9) s (p < 0.001). Comparing the second Melker insertion with the surgical airway, the difference was − 37.5 (20.8) s (p < 0.0001).

With the Melker uncuffed tube, 26/27 volunteers achieved successful ventilation at the first attempt and all by the second attempt. With the Melker cuffed tube, 25/27 were successful at the first attempt and all by the second attempt. With the surgical airway, 23/27 succeeded at the first attempt, three at the second attempt and all by the third attempt. There were no significant differences in failure rates at the first attempt between the three groups (p = 0.25). There were no failures in any of the techniques at the first attempt amongst the consultant group, compared with seven failures by other grades, a significant difference (p = 0.04). For the surgical airway, the difference in failures between consultants and juniors did not reach significance (p = 0.07). All failures were due to tube misplacement. With the Melker tubes, failure was due to lateral deviation off the larynx. In the case of the surgical attempts, two failures were due to lateral deviation and two to cranial misdirection of the tube.

There was no significant difference in the subjective ease of insertion (p = 0.18).

After the study, seven of the 11 consultants (64%) preferred the surgical approach and 10 of the 16 non-consultants (63%) preferred the wire-guided technique, a significant difference (p = 0.04). All participants felt more confident in their ability to perform either procedure in an emergency.

There were no significant differences on standard ventilator settings between the ventilation achieved with the 5.0-mm cuffed Melker and 6.0-mm cuffed surgical airway (Table 2): (mean (SD) airway pressure (28 (4.5) vs. 27.3 (5) cmH2O, p = 0.60); mean (SD) tidal volume (436 (52) vs. 446 (41) ml, p = 0.49) and mean (SD) minute volume (6.56 (0.72) vs. 6.52 (0.50) l.min−1, p =0.83). With the uncuffed Melker tube, substantially less ventilation was achieved compared with the cuffed tubes (p < 0.001), manual obstruction of the upper airway producing an increase in mean (SD) tidal volume (19 (5) vs. 89 (67) ml, p < 0.001). Maximum hand-ventilation with the self-inflating bag and the uncuffed Melker achieved a further modest increase in mean (SD) tidal volume to 145 (56) ml (p < 0.001), but a much greater increase in mean (SD) minute volume to 6.5 (1.6) l.min−1 (p < 0.001) by virtue of the greater respiratory rates achievable. With manual ventilation, maximum minute volumes were comparable to those achieved with the cuffed tubes and the Nuffield ventilator. Attempted manual obstruction when using the self-inflating bag produced no significant increase in mean (SD) tidal volume (145 (56) vs. 164 (77) ml, p = 0.39) or mean (SD) minute volume (6.5 (1.6) vs. 7.4 (3.2) l.min−1, p = 0.27).

Table 2.   Ventilation indices comparing Melker uncuffed with and without attempted upper airway obstruction, Melker cuffed and surgical cricothyroidotomy. Values are mean (SD).
 Melker uncuffedMelker uncuffed (obstructed)Melker cuffedSurgical 
  • *

    Melker uncuffed vs. Melker uncuffed (obstructed).

  • Melker uncuffed (obstructed) vs. Melker cuffed.

Mechanical ventilation
 Tidal volume; ml  19 (5)  89 (67) 436 (52) 446 (41)p < 0.001* p < 0.001
 Minute volume; ml.min−1 282 (75) 875 (531)6559 (715)6524 (496)p < 0.001* p < 0.001
 Airway pressure; cmH2O   0.8 (0.3)   2.8 (2.8)  28.0 (4.5)  27.3 (5)p = 0.002*
Maximum hand ventilation
 Tidal volume; ml 145 (56) 164 (77)p = 0.39*
 Minute volume; ml.min−16526 (1576)7387 (3227)p = 0.27*

Discussion

  1. Top of page
  2. Summary
  3. Method
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

Emergency cricothyroidotomy is the final step of all algorithms for the ‘can’t intubate, can't ventilate' scenario [1] and as such should be a core skill for anaesthetists of all grades [1, 10]. Patients are likely to be profoundly hypoxic prior to cricothyroidotomy [10] and it is therefore essential that the chosen technique establishes an airway as quickly and as effectively as possible, with large tidal volumes, so that oxygenation can be rapidly restored [1, 10].

Needle cricothyroidotomy and high pressure jet ventilation should reverse hypoxia rapidly [2, 3, 11], but at the expense of an unprotected airway and a substantial risk of barotrauma [3, 12]. Surgical cricothyroidotomy with a cuffed tube is an alternative, which some consider to be the ‘gold standard’[10], allowing conventional ventilation to be rapidly established [13], but with a significant surgical complication rate [6, 14]. Purpose-built kits have therefore been designed to place a tube in the trachea using a Seldinger wire-guided approach, with which most anaesthetists are familiar [5–10]. Until recently, these have only been available as uncuffed devices, so that the airway remains unprotected, gas leaks are inevitable, ventilation is suboptimal [1, 4, 10] and complications still occur [7]. Compared with surgical cricothyroidotomy, Chan et al.[6] found that insertion times were similar, but there were more complications with the surgical approach. However, Eisenburger et al.[7] demonstrated that the wires could kink and surgical access was quicker. Neither study assessed ventilation.

Vadodaria et al.[5] concluded that the 4.0-mm uncuffed Quicktrach (VBM Medizintechnik, Tuttlingen, Germany) restored oxygenation more quickly than the uncuffed 4.0-mm Melker in a simulation of ‘can’t intubate, can't ventilate'. Fickers et al.[15] compared the Quicktrach with the 4.0-mm Mini-Trach II (Smiths Medical Ltd, Hythe UK), a Seldinger wire guided technique, favouring the Quicktrach. However, Craven and Vanner [4] showed in a laboratory study that the Quicktrach does not allow sufficient ventilation in an unobstructed airway because of gas leakage, particularly when proximal resistance was low, favouring the 6.0-mm uncuffed Melker. These results suggest that uncuffed tubes of 4.0 mm or less can no longer be recommended in the ‘can’t intubate, can't ventilate' situation [1, 10]. It has been suggested that the proximal gas leakage can be prevented by manual obstruction of the upper airway, [4] but this has not been formally studied and requires an additional, potentially unreliable, manoeuvre in a crisis situation.

For ‘can’t intubate, can't ventilate' situations the most appropriate choice has therefore been between needle cricothyroidotomy, an uncuffed 6.0-mm Melker or surgical cricothyroidotomy with a cuffed tracheal tube. This study has shown that a 5.0-mm cuffed Seldinger wire-guided Melker tube is superior to the uncuffed option in a laboratory setting. Despite surgical cricothyroidotomy being significantly faster than either of the wire-guided techniques, over half the anaesthetists still preferred the wire-guided system. The stated reasons were familiarity with the Seldinger technique and a concern that bleeding or laryngeal movement might make the surgical procedure more difficult in the clinical situation. Those who preferred the surgical airway cited the speed and simplicity of the technique.

The mean improvement of 11.2 s (p < 0.01) between the first and second of the two wire-guided insertions demonstrates that learning had occurred. It is possible that, with more practice, the difference in insertion time between wire-guided and surgical cricothyroidotomy might reduce. However, neither the demonstrator nor any of the volunteers were able to insert the Melker device in less than 52 s, whilst three volunteers completed the surgical technique in 27 s.

We have demonstrated no significant difference between the cuffed and uncuffed Melker devices in terms of time or difficulty of insertion, but we have found a major difference in the ability of the two devices to achieve adequate ventilation. Even when upper airway occlusion was simulated by manual occlusion and ventilation was maximised using a self-inflating bag, the tidal volumes obtained were only equivalent to anatomical dead space. Compared with other commercially available devices, such as the 4.0-mm Quicktrach, the 6.0-mm uncuffed Melker is a relatively large calibre airway and might therefore be expected to allow reasonable ventilation, as reported by both Craven and Vanner [4] and Vadodaria et al.[5]. In both those studies, upper airway obstruction was simulated in an approximation of the expiratory obstruction likely to be present with an unsupported upper airway. However, in our study, ventilation was inadequate because proximal gas leakage could not be eliminated. It is possible that performance might be improved in the clinical situation and that our model was unrepresentative in this respect. However, it is also possible that this manual method of obstruction may not restore sufficient ventilation when an uncuffed tube is selected and may promote gastric distension, regurgitation and aspiration. Our test lung was set to 20 ml.cm−1 H2O, which may have been relatively compliant compared to a patient with intrinsic lung pathology, when proximal gas leakage would be exacerbated. It may be essential to achieve upper airway obstruction if uncuffed tubes are inserted and alternative techniques might be considered, such as a tightly fitting throat pack. This would add to the time taken to achieve worthwhile ventilation.

This laboratory study used a model that is unlikely to reproduce in full the circumstances of a real clinical airway emergency. In particular, the anatomy and ‘feel’ of the tissues were markedly different to the human. The clinical scenario would also be likely to be accompanied by difficult anatomy, a mobile larynx, bleeding, hypoxia and extreme operator anxiety. In these circumstances, there is much to commend a technique that is intrinsically familiar, such as the Seldinger approach. However, whatever technique is chosen, it is essential that adequate training has taken place and this model was useful in this respect. The 11 s reduction in time to achieve a wire-guided airway between first and second attempts is testimony to the value of practice. All candidates felt more confident in their ability to obtain a surgical airway after their training and assessment. A substantial proportion of the wire guided insertion time was taken up by placement of the cannula and wire. If difficulty is anticipated, a cannula could be placed pre-emptively [16]. It could be used as a conduit for jet ventilation rapidly to restore oxygenation and then could be converted to a cuffed Melker to protect the airway in a controlled manner, possibly in a similar timescale to surgical cricothyroidotomy.

It is concluded that in this laboratory study, the cuffed Melker tube takes no longer to insert than the uncuffed device, is no more difficult to use, has a similarly low failure rate, can protect the airway and allows adequate, controlled ventilation. As the Seldinger technique is preferred by non-consultants, the cuffed device should be considered for all areas where they administer anaesthesia. The uncuffed Melker tube can no longer be recommended other than as a conduit for high-pressure jet ventilation, for which faster and simpler techniques are available [11]. Surgical cricothyroidotomy is considerably quicker than the Seldinger technique and this may be clinically significant when hypoxia is profound. This technique is preferred by consultants, but may have a higher failure rate in inexperienced hands.

Acknowledgements

  1. Top of page
  2. Summary
  3. Method
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References

The authors are grateful to Dr S. Singh, Consultant Anaesthetist, and to Mr Stuart Eccles of the Electrical, Biometric and Mechanical Equipment department of the Countess of Chester hospital, for their assistance. We are also indebted to Cook Medical Ltd, who supplied the Melker kits and additional guidewires free of charge.

References

  1. Top of page
  2. Summary
  3. Method
  4. Results
  5. Discussion
  6. Acknowledgements
  7. References